Ancestry deconvolution refers to identifying the ancestral origin of chromosomal segments in individuals. Ancestry deconvolution in admixed individuals (i.e., individuals whose ancestors such as grandparents are from different regions) is straightforward when the ancestral populations considered are sufficiently distinct (e.g., one grandparent is from Europe and another from Asia). To date, however, existing approaches are typically ineffective at distinguishing between closely related populations (e.g., within Europe). Moreover, due to their computational complexity, most existing methods for ancestry deconvolution are unsuitable for application in large-scale settings, where the reference panels used contain thousands of individuals.